The present invention relates to an improved pump for pumping molten metals and is directed to means for controlling leakage about the drive shaft of the pump by causing metal flowing axially along the said shaft to solidify in a cooled annulus formed about the shaft to provide an effective seal. More particularly, this invention relates to an improved pump having means for sealing about the drive shaft of a gear pump used to lift molten lead or lead alloy from a melting furnace to a casting trough from which a rotating cooled drum removes sheet metal.
U.S. Pat. No. 2,864,314 provides a face-type shaft sealing assembly for a pump which handles hot fluids. One shaft-mounted face-seal member is urged by spring means against a second, housing-mounted, face-seal member. They coact to divide the interior of the pump housing into a pumping zone and a sealed chamber. A small fraction of the fluid being pumped passes through the sealing means, which is cooled, to lubricate the faces of the assembly.
Canadian Pat. No. 896,312 provides for the forming of an ice seal between the rotating shroud and the stationary housing of a turbine. The ice is initially formed when the turbine is not operating or chips of ice or other low-friction material are introduced into the sealing space during operation.
In both the foregoing patents, the fluid being pumped is used to provide sealing means. However, molten lead solidifies on cooling and its passage between relatively rotating face-sealing members would be impractical. In addition, solidification of lead on a stationary shaft would prevent start-up of the pump.
In the casting of lead alloy sheet as described in co-pending U.S. Pat. application No. 367,143, a smooth and steady flow of molten metal through a trough in which the periphery of a casting drum moves is essential to produce uniform cast sheet metal. Pulsating action, such as from a centrifugal pump, tends to aerate the molten metal and to promote undesirable drossing of active metal alloying additives such as calcium. The positive displacement action of a gear pump provides such desired smooth flow of molten metal from a melting furnace to the casting trough and, for easy access to the pump for maintenance, the pump preferably is mounted externally on the furnace wall. The pump is reversible, permitting immediate removal of molten metal from the casting trough and from piping in communication therewith at the end of a casting operation.